RE: Human Survival
July 30, 2013 at 7:39 pm
(This post was last modified: July 30, 2013 at 7:50 pm by Anomalocaris.)
The point isn't there is not enough water vapor in the atmosphere near the poles now. The point is even a future global water vapor green house will not be able to elevate the temperature in high latitudes near the point where complex ecosystem can no longer survive. The temperature threshold where complex ecosystem will no longer be able to survive is often tagged at 50 degrees C. The equatorial region may average well beyond 50 degrees C in a global water vapor greenhouse, but poles will stabilize well before reaching average of 50C.
Also, even a global water vapor greenhouse would probably not lead to near total loss of water to space through photo dissociation because 2 factors. 1. The rate at which water sequestered in the mantle would be outgassed onto the surface will equilibrate the loss of water into space when there would still be quite a large amount of surface water on earth. 2. The altitude which water vapor can reach in the global water vapor greehouse scenario will decrease over time as nitrogen is removed from atmosphere through geological processes, leading to overall thinning of atmosphere, and this will lead to a gradual reduction in the efficiency of photo dissociation over time even as pace of vulcanism on earth would decrease with loss of core heat.
Recent geochemical studies suggests the mantle of the earth contains from 20-100 times more water than exists on earth's surface, chemically combined in minerals. Most of the water having been there since the formation of the earth. Only 10 years ago the estimate was mantle and lower crust contained only 1-2 times as much water as the oceans, and a good deal of that was pulled into the mantle by plate subduction.
This dramatically alters estimates of the rate at which water is release to the surface through vulcanic outgassing. It is now thought volcanic outgassing will release as much water onto the surface as is currently in all of the oceans every 1-2 billion years or so. Currently plate subduction is though to remove water from the oceans by dragging waterlogged sediments into the mantle as roughly the same rate. But plate tectonics will likely come to a stop long before vulcanism on earth comes to a stop. So the mantle is expected to become a major and damned near inexhaustable net contributor of surface water in a billion years or so.
Also, even a global water vapor greenhouse would probably not lead to near total loss of water to space through photo dissociation because 2 factors. 1. The rate at which water sequestered in the mantle would be outgassed onto the surface will equilibrate the loss of water into space when there would still be quite a large amount of surface water on earth. 2. The altitude which water vapor can reach in the global water vapor greehouse scenario will decrease over time as nitrogen is removed from atmosphere through geological processes, leading to overall thinning of atmosphere, and this will lead to a gradual reduction in the efficiency of photo dissociation over time even as pace of vulcanism on earth would decrease with loss of core heat.
Recent geochemical studies suggests the mantle of the earth contains from 20-100 times more water than exists on earth's surface, chemically combined in minerals. Most of the water having been there since the formation of the earth. Only 10 years ago the estimate was mantle and lower crust contained only 1-2 times as much water as the oceans, and a good deal of that was pulled into the mantle by plate subduction.
This dramatically alters estimates of the rate at which water is release to the surface through vulcanic outgassing. It is now thought volcanic outgassing will release as much water onto the surface as is currently in all of the oceans every 1-2 billion years or so. Currently plate subduction is though to remove water from the oceans by dragging waterlogged sediments into the mantle as roughly the same rate. But plate tectonics will likely come to a stop long before vulcanism on earth comes to a stop. So the mantle is expected to become a major and damned near inexhaustable net contributor of surface water in a billion years or so.
